1. Field of the Invention
The present invention pertains to a respiratory patient interface used to deliver gas to a user. In particular, the present invention is related to a respiratory patient interface having a cushion with a flap having a frustum-shaped portion.
2. Description of the Related Art
Obstructive sleep apnea or OSA, obstructive sleep hypopnea, and upper airway resistance syndrome (UARS) are among a variety of known disorders characterized by episodes of complete or partial upper airway obstruction during a state of diminished consciousness, such as sleep, anesthetization, or post anesthesia. OSA, hypopnea, and UARS cause intermittent interruption of ventilation during sleep with the consequence of potentially severe oxyhemoglobin desaturation. Typically, those afflicted with OSA, hypopnea, and UARS experience repeated, frequent arousal from sleep in response to the oxygen deprivation. The arousals result in sleep fragmentation and poor sleep continuity.
Consequences of OSA, hypopnea, and UARS may include debilitating daytime sleepiness and cognitive dysfunction, systemic hypertension, cardiac dysrythmias, pulmonary arterial hypertension and congestive heart failure. Other consequences may include a predisposition to myocardial infarction, angina pectoris, stroke, right ventricular dysfunction with cor pulmonale, carbon dioxide retention during wakefulness as well as during sleep, and continuous, reduced arterial oxygen tension. Moreover, the cognitive impairment resulting from OSA, hypopnea, and UARS puts those afflicted at elevated risk of accidents.
The pathogenesis of the airway obstruction that characterizes OSA, hypopnea, and UARS can include both anatomic and functional abnormalities of the upper airway that result in increased airflow resistance. Such abnormalities may include narrowing of the upper airway due to suction forces created during inspiration, the effect of gravity pulling the tongue back to oppose the pharyngeal wall, and insufficient muscle tone in the upper airway dilator muscles, among others. It is also believed that excessive soft tissue in the anterior and lateral neck, as commonly observed in obese persons, can apply sufficient pressure to internal structures to narrow the upper airway and restrict airflow.
Conventional treatment of OSA, hypopnea, and UARS has included surgical intervention, such as uvalopalotopharyngoplasty, gastric surgery for obesity, mandibular advancement procedures, maxillo-facial reconstruction, and tracheostomy. However, surgery potentially involves considerable risk of post-operative morbidity and mortality. In addition, the failure rate of surgery is disturbingly high. Pharmacological therapy has also been proposed to treat OSA, hypopnea, and UARS; however, results have been generally disappointing.
More recently, continuous positive airway pressure (CPAP) or bi-level positive airway pressure applied during sleep has been used to treat OSA, hypopnea, and UARS patients. Positive pressure is applied in the upper airway to splint or support the airway, thereby preventing its collapse and the resultant airway obstruction. A typical positive airway pressure device comprises a gas source (e.g., a blower, gas storage container) that delivers gas via a delivery conduit to a patient interface, such as a mask. It is also known to deliver the positive airway pressure therapy as a continuous positive airway pressure (CPAP), a variable airway pressure, such as a bi-level pressure that varies with the patient's respiratory cycle, or an auto-titrating pressure that varies with the monitored condition of the patient. Pressure support therapies are also provided to treat other medical and respiratory disorders, such as Cheynes-Stokes respiration, congestive heart failure, and stroke.
There are a multitude of patient interfaces known in the art. For instance, masks that provide a seal between the gas source and the patient are common. These interfaces may include prongs which fit into the nares of the patient, nasal masks which fit over the patient's nose, full face masks that fit over the mouth and nose, and total masks which fit over the patient's entire face. For any of these devices to be effective, two competing goals often need to be balanced: comfort and functionality. The comfort of the mask may be increased by reducing the area of contact between the mask and the patient; or use of a soft, lightweight, flexible material. In contrast, to enhance functionality, it would be preferable to construct the mask from a rigid, sturdy material with a large contact area between the mask and the patient to reduce the potential for failure.
One mask which attempts to balance the competing goals of comfort and functionality is disclosed in U.S. Pat. No. 4,907,584 (“the '584 patent”). The subject matter of which is hereby incorporated by reference. This mask has a rigid support portion and a cushion. The cushion includes a flexible flap having an L-shaped cross-section such that the flaps face approximately towards one another. Although the '584 patent has substantially advanced the art, it could still be further improved upon. For instance, it has been found that for some users, the flaps may not smoothly roll inwardly. Instead, the flaps may crumple or buckle resulting in areas that may not make an effective seal.
Another mask is disclosed in U.S. Patent Application Publication No. 2006-0130844. The subject matter of which is hereby incorporated by reference. This mask has an outer shell coupled to a cushion which includes a coupling portion, a middle portion, and a flap portion. The coupling portion couples the cushion to the outer shell; the middle portion provides clearance between the flaps and the coupling portion; and the flap portion has flaps that are inwardly directed such that they face one another. However, unlike the mask disclosed in the '584 patent, this mask includes a variety of features to vary the amount of support and/or sealing provided by the cushion to balance the competing goals of comfort and functionality locally. In some locations, more support may be required. In other areas more flexibility may be required. This application discloses several alternatives to achieve this goal. For instance, the cushion may include one or more pleats, the wall thickness may be varied to adjust the amount of support, or flexibility may be adjusted portionally about the cushion. Although an improvement, this device still utilizes inwardly directed flaps which may not form an optimum seal on some users. Instead, the flaps may tend to crumple or buckle.
The above-disclosed references disclose masks with inwardly directed flaps; however, masks are also known in the art which have flaps that are directed outwardly to form a trumpet-like shape. In U.S. patent application Ser. No. 11/585,320, the contents of which are hereby incorporated by reference, the mask includes flaps which are curved outwardly to provide additional clearance for the internal nasal pillows. Although effective, outwardly directed flaps still suffer from many of the same drawbacks noted above with respect to masks with inwardly directed flaps. Instead, the flaps will tend to buckle resulting in portions that may not make an effective seal.
Although all of these masks disclose features that enhance the art, addressing the competing goals of comfort and seal integrity continues to be a significant issue.